Due to the strength for holding the whole pair of rimless eyeglasses comes from the lens itself, we need to strongest lenses such as polycarbonate and other high index lenses. But for semi rimless eyeglasses, it is not a problem to resin lenses like CR-39, as the top portion of the frame and the bottom nylon string can hold the lenses tightly through the groove the edge of lenses. However, it also has some disadvantages. If you have a very low prescription, the lenses corresponding to your rx entered has a much thinner edge to put the required groove in, it will be too difficult to install. Such as: one people’s PD is 59mm, but he selected a large shape half-rim eyeglass frame which has size at 58-18-135. After measured, it is a very complex technical, and moreover, the progressive or bifocal lens is unavailable with DIA. 76mm.